Process and apparatus for casting utilizing gas stream



July 30, 1963 KAZURO SUZUKI ETAL 3,099,052

PROCESS AND APPARATUS FOR CASTING UTILIZING GAS STREAM Filed Oct. 28, 1959' FE. 1- I F/EB- 1 6 IN VEN TOR.

United States Patent 3,099,052 PRGCESfi AND APPARATUS FOR CASTENG UTKUZTNG GAS STREAM Kazuro Suzuki, Naruo, Nishinomiya-shi, Hyogo-ken, and Hiroshi Yamacka, Kadoma-cho, Kitakawaehi-gun, )salra-fu, .lapan, assignors to Sumitomo Kmzolru 'ogy'o Kabushilsi Keisha, Osaka-ski, Japan, a corporation of Japan Filed Get. 28, 1959, Ser. No. 849,228 7 Claims. (Cl. 2273) This invention relates to processes for casting metals.

It is well known that blow holes may be produced in a casting when the casting is efiected in a mold which is permeable to air such as, for example, in a sand mold or a shell mold.

The appearance of these blow holes is due partly to the presence of air in the mold and partly to the generation of organic gases and steam which are produced through the decomposition of organic materials and evaporation of moisture contained in the material forming the mold when the mold comes into contact with hot molten metal. The molten metal may be introduced into a mold under pressure and cooled to form a thin layer of consolidated metal at the boundary surface of the molten metal where contact is made with the cold surface of the mold. However, the layer is so thin that it is easily broken to permit the intrusion of gas into the casting if the pressure of gas exceeds the weight of the molten metal at that point.

As the level of the molten bath in the mold rises, the weight of the molten metal increases at the bottom of the bath, but it is dways nil at the top level of the bath. The back pressure of the gas surrounding the introduced bath, however, has its maximum value at a point a little below the top level of the bath. The reason for this is that, at any point far below the top level, the produced gas has had suificient time for going away from the point, passing through the spaces between the grains forming the mold or intruding into the molten bath. Thus the point of the highest back pressure of gas rises as the level of bath rises.

This point and the value of the highest pressure of gas as well as the weight of molten metal vary, depending on the kind of metal and the type of a mold used. For instance, when a shell mold is used and a low carbon steel bath is introduced at the rate of 500 g./sec., the maximum back pressure of gas may appear at a point near the top level of the bath where said level has passed 2.5-3.0 'seconds before and the value of the back pressure may be in the order of 7-8 mm. water column.

With a green sand mold, the maximum back pressure on the boundary surface may appear after seconds and the value may be in the order of 20-25 mm. water column.

We do not desire to limit the present invention by theoretical explanation and believe that there may be some further reasons for the intrusion of gas in addition to the relationship between the back pressure of gas and the weight of molten metal. These may include, for example, the turbulent condition at the top of the molten .bath and the surrounding part thereof when the bath is introduced into its mold.

When a sample piece is inspected after solidification, blow holes are particularly concentrated in the upper part of the piece. This is considered to be due to the fact that gas produced from the mold by the rapid increase of temperature has the tendency to float towards the top of the bath and thus the formation of blow holes in the lower part of the bath is greatly decreased. Some of the gas bubbles which have proceeded to the top part cannot pass through the top surface and are entrapped and retained to form blow holes.

In relation to the invention, it is believed that if the disturbed gas surrounding the top part of the bath were 3,099,052 Patented July 30, 1963 "ice to be carried away from the surface of the bath by a gas stream and were to be removed from the mold, the intrusion of gas into the mold would be decreased greatly and the appearance of blow holes would be minimized. Based on this idea, it has now been found that the provision of a gas stream in a casting mold is very useful for the prevention of the formation of blow holes in castings and that such a gas stream can be conveniently provided by using high pressure or vacuum.

An object of the present invention is to prevent the appearance of blow holes by forming a stream of air or gas flowing in a predetermined direction in each part of a mold before casting, and maintaining such gas stream during casting to carry away steam and gases produced in the mold.

For better understanding of the present invention, reference is next made to the accompanying drawing in whichz FIG. 1 is a schematic side sectional view of an apparatus for casting employing a gas stream caused by reduced pressure;

FIG. 2 is a schematic side sectional view of an apparatus for casting employing a gas stream caused by increased pressure; and

FIG. 3 is a schematic view of a shell mold to which the present invention using vacuum is applied.

7 In the embodiment of FIG. 1, 1 represents a vacuum vessel connected to pipes 3 through which gas in the vacuum vessel 1 can be evacuated by means of a suction pump or a blower (not shown). The top of the vacuum vessel 1 is open in the drawing but may be covered With a perforated plate. 7

On the vacuum chamber 1 is placed a moldz which has a bottom plate 4 provided with a number of small holes to allow passage of the gas from the mold. The mold has a cavity 6 into which molten metal is introduced from a gate 7. The mold 2 is closed excepting for the openings of the gate, the top of the cavity Gand the holes of the bottom plate, and a sealing or packing ring 8 is provided between the mold 2 and the vacuum vessel 1. The mold is constituted by green sand and there are spaces between the sand grains. In the operation, the vacuum pump or blower connected to the suction pipes 3 is op erated to establish a vacuum in the vessel 1. Air in the mold is drawn into thevessel 1 and air or some other gas is drawn into the mold 2 via the top of the cavity 6 and enters the vacuum vessel '1 through the spaces between the sand grains. Thus a gas stream having a control-led direction is created. Under this condition, molten metal is introduced from the gate into the cavity 6 of the mold 2.

When the molten metal comes into contact with the Wall of the cavity 6 and moisture and organic material contained in the sand of the mold are vaporized by heating, the vapor is carried away by the gas stream in the direction as shown by arrow a in the vicinity of the top of the molten bath and then passes toward the bottom 4 to be discharged through the vacuum vessel 1 and the pipes 3 outside of the mold. The intrusion of gas into the molten bath is thus greatly lessened to produce a casting substantially free from blow holes. The gas to be introduced into the mold 2 may be air or an inert gas such as argon or neon.

In the above, a vacuum is used or creating the desired gas stream, but a gas stream may also be obtained by using gas under pressure. FIG. 2 illustrates one of the embodiments of such an apparatus wherein the side wall and the bottom of the mold 2' are provided with a number of small holes and a :blast pipe '9' is attached to the top of the cavity 6' to introduce air or an inert gas under pressure into the mold by means of a blower, a compressor, a gas bomb, etc. (not shown) connected to the blast pipe 9. The gas under pressure introduced into the mold 2" is discharged outside of the mold passing through the spaces between the sand grains forming the mold. When molten metal is introduced via a gate 7 and comes into contact with the wall of the cavity,'the steam and vapor produced are carried away by a gas stream (see arrow a) flowing toward the outside of the mold.

FIG. 3 illustrates a case where a shell mold is used for casting. In the drawing, represents a shell mold which is arranged in a mold casing. The mold casing has a side wall 12" having a number of small holes or being substantially gas permeable and the inside of the mold casing is in communication with a vacuum chamber 1" surrounding the mold casing through the side wall.

' The vacuum chamber is provided with suction pipes 3", and gas in the vacuum chamber is drawn out through the suction pipes 3" by means of a vacuum pump, a blower or the like (not shown) connected to the suction pipes. When vacuum is established in the vacuum chamber 1", air or gas in the mold is drawn into the vacuum chamber while or gas is allowed to enter the mold from the top of the cavity 6" of the shell mold 10". Air or gas entering the mold will pass through the shell of the mold 10" and the spaces between the steel shot filling the space between the wall of the shell mold 10" and the wall of the mold casing 11" to enter the vacuum chamber 1" and to be discharged through the suction pipes 3" to the outside of the mold. Thus a gas stream having a direction (see arrow it) toward the outside of the mold casing is established and steam and vapor produced when a hot molten bath is introduced via a gate 7 into the cavity 6" of the mold can be carried away as in the cases of FIG. 1 and FIG. 2.

In all of the embodiments mentioned above, the gas introduced into the mold may be air but, when an inert gas such as argon or neon is used, the generation of oxides can be prevented during casting and consolidation after casting and, therefore, it is advisable to use such a gas in some cases in order to obtain a casting having a specially good surface. 7

In the following, examples of the application of the process of the present invention will be explained. These examples show that when the casting process of the invention employing a gas stream is used for the production of a casting, the appearance of blow holes can be prevented even to a green sand mold is added 6% water or a shell mold is used which generally involves the formation of many blow holes.

Example 1 A number of steel castings are manufactured by using the mold of FIG. 3, varying the rate of gas stream flow. After casting, a flat surface of the casting was cut to a depth of 3 mm. and inspected for blow holes.

The shell mold was soaked in water :for 48 hours after the tormaton of the mold and 4% water was absorbed by the mold. This soaking increased the tendency to form blow holes by increasing the production of steam at the time of contact with hot molten metal. Nevertheless, the appearance of blow holes was very little when casting was carried out according to the present invention, and particularly when the rate of the stream flow was high. I The rate of the stream flow was measured immediately before the introduction of molten bath into the mold, and this flowing condition was maintained during the whole course of the introduction of molten bath.

It is to be noted that many blow holes are produced in casting by conventional process, but blow holes were greatly reduced in the castings produced by the process of the present invention, particularly when the rate of the stream flow was increased.

i In one case, a vacuum of 180 mm. was provided, but no suction was applied and the rate of stream flow was made nil at the time of casting. Under such conditions, a substantial quantity of blow holes was produced show- .4 ing that casting with a gas stream caused by reduced pressure is difierent from casting under reduced pressure. Conditions adopted in Example 1 were as EEOllOWSZ (a) Process Gas stream process (reduced pressure) excepting the case of the conventional process.

(b) Gas introduced Air.

(c) Mold A shell mold soaked in water for 48 hours.

(d) Size of mold 350 mm. x 250 mm.

(e) Dimension of product mm. x 70 mm. x 25 (1) Weight of product 4 kg.

(g) Material of product SC. 455

(h) Pressure in mold 0-190 H O.

(i) Rate of stream flow before the introduction of molten metal Varied within the range of 0-13.70 cc./min.cm.

*SC. 45 is a Japanese standard of steel and has the following contents of various elements:

0 Si Mn P s Cr Example 2 A casting was produced by the process of the present invention in which a gas stream was caused by using a high pressure. The detailed conditions in this casting were as follows:

(a) Process Conventional process and gas stream process under pressure.

(b) Gas introduced Air.

(0) Mold Green sand mold (containing 6% moisture).

(d) Size of mold 200 mm x mm.

(e) Dimension of product 100 mm x 50 mm.

(1) Weight of product 4 kg.

(g) Material of product SC. 45.

(h) Pressure in mold 50 mm. water column.

(i) Rate of stream before the introduction of molten metal 3 l/sec./cm.

ducing a molten metallic substance into a mold permeable ,to air through an inlet at the bottom of the mold so that the substance rises in the mold, and blowing a pneumatic medium continuously through an opening at the top of the cavity into the mold in a manner such that said medium runs substantially counter to the rising substance until the mold is filled with said substance, and produces a pneumatic current of a fixed flow rate, which current passes continuously through the mold to carry away gas produced within the mold.

2. A process according to claim 1 wherein zones of reduced pressure are provided at the bottom and sides of the mold on an air stream of a fixed flow rate passing outwardly through the mold wall is produced by continuously reducing the pressure in the zones of reduced pressure.

3. A process according to claim 1, wherein a blast pipe is connected to the top of the mold, a pneumatic stream into the mold is produced by continuously introducing said medium via the blast pipe.

4. A process according to claim 1, wherein the medium introduced into the mold is an inert gas.

5. A process according to claim 1, wherein the air permeable mold is constructed of sand.

6. A process according to claim 1, wherein the air permeable mold is a shell mold.

7. Apparatus for casting metal which comprises a mold of air permeable material and means defining chambers of reduced pressure on the side and the bottom of the mold, said chambers being connected with the mold due to the permeability of the latter, said mold being upwardly open to the atmosphere and having an inlet at the bottom thereof, and an exhaust pipe coupled to said chambers.

References Cited in the file of this patent UNITED STATES PATENTS 672,447 Lustig Apr. 23, 1901 901,547 McCarty Oct. 20, 1908 10 2,778,077 Andrews Jan. 22, 1957 2,826,489 Wagner Mar. 11, 1958 2,893,860 Lorenz July 7, 1959 2,908,054 Wilkins Oct. 13, 1959 

1. A PROCESS FOR CASTING METAL WHICH COMPRISES INTRODUCING A MOLTEN MATALLIC SUBSTANCE INTO A MOLD PERMEABLE TO AIR THROUGH AN INLET AT THE BOTTOM OF THE MOLD SO THAT THE SUBSTANCE RISES IN THE MOLD, AND BLOWING A PNEUMATIC MEDIUM CONTINUOUSLY THRUOGH AN OPENING AT THE TOP OF 